i am not a lawyer Marco, but i run the business with 19 employees at this moment.
checked together with my "contable" around 3 weeks ago for a friend of her's, we requested from the oficina de trabajo in higuey the lump sum for both cases, and got the answer back that with that 28 day preadvise it would be the same than if she got "kicked".
but that's just been a check in one case and not for one of my own employees, so i've not been that hard on details for the case.
my own personel practice is that someone who i have to quit for what ever reason gets what i will be told by the oficina de trabajo.
if someone quits for a good reason, found a good job off the water, secretary who wants to take some time to take care of the house/family aso, in those cases i will pay even up to more than a paper would say, i am within my own small world not in that kind of "Boss-Slave" relationship, a good employee is the one who brought me good money, so keep him happy and he will give you a hand in what ever situation needed even when employed by a competitor at that future moment.
but that's just behavior, no official law.
Mike